The present invention relates to a clean room and typically to a clean room in which semiconductor devices or the like are manufactured.
As a conventional clean room for manufacture of semiconductor devices, a clean room as shown in FIG. 3 has been known (Japanese Patent Laid-Open Publication H10-96332). A whole area of a clean room 101 is divided by a partition 101c into a first area 101a and a second area 101b having air conditioning systems independent of each other. A manufacturing apparatus 114a, a conveying apparatus 127, a storage apparatus 128 and the like are installed in a working zone 126a that is subjected to air conditioning in the first area 101a. On the other hand, a manufacturing apparatus 114b that generates chemical mist is installed in a working zone 126b that is subjected to air conditioning in the second area 101b. In the first area 101a, air from an external air conditioner 111 in which the air has been subjected to dust removal and humidity control as well as chemical-free air from chemical-free air feeding apparatus 123 in which the air becomes free of chemically reactive components, together with described-below circulating air, are fed into the working zone 126a through a ceiling chamber 124a, fan filter units 125 having chemical filters 112 and non-chemical filters 130a. The non-chemical filters 130a are HEPA (High Efficiency Particulate Air) filters and ULPA (Ultra Low Penetration Air) filters and the like. Air fed into the working zone 126a is forwarded through a grating floor 107a (a floor shaped like a draining board) down to a utility zone 129a. The air is then returned to the ceiling chamber 124a via the utility zone 129a through a temperature controlling apparatus 132a, a circulating fan 131a and a circulation duct 109a. In the second area 101b, air from the external air conditioner 111 in which the air has been subjected to humidity control, together with the described-below circulating air, is fed through a ceiling chamber 124b and non-chemical filters 130b into the working zone 126b. Air fed into the working zone 126b is forwarded through a grating floor 107b down to a utility zone 129b and is then returned to the ceiling chamber 124b via the utility zone 129b through a chemical filter 110, a temperature controlling apparatus 132b, a circulating fan 131b and a circulation duct 109b. As a result, most of air fed into the first area 101a and the second area 101b circulates only in the first area 101a and only in the second area 101b, respectively. Part of air fed into the working zones 126a, 126b is discharged from the clean room 101 through ducts (not shown) by local ventilators installed in the manufacturing apparatus 114a, 114b and the like. This arrangement is intended for preventing cross contamination between the area 101a and the area 101b. 
In the conventional clean room 101, however, the manufacturing apparatus 114a, the conveying apparatus 127, the storage apparatus 128 and the like exist together in one working zone 126a where air circulates. Accordingly, dust such as particulate produced from anywhere in the working zone 126a might contaminate an exposed semiconductor wafer that has been transferred from the conveying apparatus 127 to the manufacturing apparatus 114a. 
In the first area 101a, air that has passed through the chemical filters 112 and air that has passed through the non-chemical filters 130a mix with each other in a circulation process in the working zone 126a and in later processes, so that loads on the chemical filters 112 increase. This is because chemical mist (atoms or ions of sodium, potassium, aluminum, iron, cobalt, nickel, copper, ammonia and the like) that causes chemical contamination is generated not only from the manufacturing apparatus but also by conveyance of objects and movement of workers in the working zone 126a. Loads on the chemical filter 110 is also increased in the second area 101b because the chemical filter 110 is passed through by air from the whole area of the working zone 126b, that is, air not only from an area for the manufacturing apparatus 114b but also from an area for workers moving around the apparatus. As a result, the chemical filters 112 and 110 have to be replaced frequently, for example, at intervals of several months to several years. A running cost of the chemical filters is thereby increased.
The non-chemical filters 130a and 130b such as HEPA and ULPA make little problem on running cost, because unit costs of such non-chemical filters are not higher than about one-third of those of chemical filters and because replacement frequencies of non-chemical filters may be smaller than those of chemical filters.